A. Technical Field
This invention generally relates to pressure activated engines. More particularly, this invention is a reciprocating-piston engine having a harmonic oscillator valve controlling the admission of a pressurized expansible fluid into an expansion chamber and a spring-loaded outlet valve controlling the exhaust of lower pressure fluid from the expansion chamber.
B. Description of the Related Art
Engines that transform the internal energy within a high-pressure expansible fluid into useful mechanical energy are well known. Perhaps the earliest and best known is the steam engine. Central to the operation of such an engine is the valve mechanism that controls the admission of high-pressure fluid into an expansible chamber and the release of low-pressure fluid from the expansible chamber. The power and efficiency of such an engine is strongly driven by the phasing of the opening and closing of the inlet and outlet valves. Maintaining high efficiency under a variety of steam pressure conditions and operating speeds requires changing the timing or cutoff of the valves, and a number of mechanisms are known to achieve such variable valve timing. Among these are the Corliss valve mechanisms described in US6162 and US8253. With such mechanisms proper lubrication is required in order to prevent untimely wear of the sliding parts, and the relative complexity of such mechanisms is a disadvantage.
Reciprocating pneumatic engines that avoid the use of cams or sliding valves are known. In one such device, a spring loaded inlet valve is pushed open by mechanical contact with a piston, as it approaches the TDC (Top Dead Center) position, to admit high-pressure gas into a cylinder. As the piston moves towards BDC (Bottom Dead Center), an outlet port in the side of the cylinder is uncovered, and pressurized gas within the cylinder is vented to the atmosphere. Such engines are mechanically quite simple, but suffer from relatively low efficiency, primarily because on the return stroke of the piston from BDC to TDC, after the outlet port is covered, the piston compresses gas trapped within the cylinder and thus robs the engine of potential power.
A recent pneumatic engine described in pending patent U. Publication No. 2011/0030548 by Andrew C. Berkun, known as a “Slam Valve Motor”, shows a normally open inlet valve, in normal operation held closed by the pressure difference between the external high pressure supply and the lower pressure within the engine cylinder until pushed open by mechanical contact with a piston, and a normally open outlet valve, pushed closed by mechanical contact with the piston. Berkun teaches that the inlet valve moves to the closed position when flow through it exceeds a critical flow rate. Attaining the critical flow required for closure of the inlet valve from its fully open position, leads to a corresponding limitation on the minimum operational speed of the engine, and this can be disadvantageous under some circumstances. This limitation of Berkun's slam valve motor is that, in order to close the inlet valve, a certain critical flow speed must be reached at some phase in the power stroke of the engine. Thus, at low engine speed, if the critical flow speed is not attained, the slam valve motor may not be able to operate.
The harmonic engine disclosed in U.S. Pat. No. 7,603,858, teaches the use of a harmonic oscillator inlet valve together with a harmonic oscillator outlet valve. In this work, a latch mechanism is incorporated in order to ensure the closure of the inlet valve after a cycle of harmonic oscillation. In this prior art, however, the ratio of the period of the inlet valve oscillator to the engine cycle period allows only a narrow range in the ratio of the inlet supply pressure to the outlet release pressure. Also, the ratio of the outlet harmonic oscillator period to the engine period may only vary slightly. As a result, there is little flexibility in the choice of the operating conditions, viz. the engine speed, the pressure ratio and the output power level.